This invention relates to a head arm for use in a magnetic disk drive and more particularly to a head arm of the kind described above which is not deformed in itself under what ever environmental conditions so as to minimize undesirable off-track of a magnetic head relative to a magnetic disk.
Capability of attaining a high information recording density is now demanded more and more for a magnetic disk drive, and, in order to attain this high information recording density, it is required that a magnetic head carried by a head arm be accurately positioned relative to a desired track on a magnetic recording medium such as a magnetic disk. On the other hand, the general-purpose usability is also demanded for the magnetic disk drive. That is, the magnetic disk drive it now frequently installed in, for example, a laboratory in addition to its usual place of installation in a room such as an air-conditioned computer room. Therefore, the head arm tends to be subjected to thermal deformation due to a variation in the temperature of the environment in which the magnetic disk drive is operated. The thermal deformation of the head arm is undesirable in that it leads to occurrence of off-track of a magnetic head relative to a magnetic disk. JP-A-61-123068 discloses a method for compensating this undesirable off-track. According to the method disclosed in the cited application, the head arm is made by integrally combining or bonding together two kinds of materials, that is, the material of the head arm and a resin material into a plurality of laminated layers so as to suitably adjust the coefficient of thermal expansion of the entire head arm in the direction of access or seek, thereby minimizing the off-track due to differential elongation of the head arm in that direction. JP-A-61-16076 discloses another method for off-track compensation.
According to the method disclosed in this application, a member having a coefficient of thermal expansion different from that of the head arm is combined with the head arm so as to form an assembly similar to a bimetal, thereby compensating the undesirable off-track by the bimetal-like function.
In the prior art method disclosed in JP-A-61-123068, the adjustment of the thermal expansion of each of the head arms in the direction of seek is only noted so as to minimize the thermal off-track due to the differential elongation. However, in this application in which the head arm is formed by bonding, to the material of the head arm, the resin which is the material different from that of the head arm, deflection of the head arm of the above structure in an out-of-plane direction due to a variation in the ambient temperature (deflection similar to that of a bimetal) is not utterly taken into consideration. In a modern magnetic disk drive, the problem of the off-track attributable to the deflection of the head arm in the out-of-plane direction is especially closed up. Also, the head arm formed by laminating a plurality of layers of different kinds of materials as described above has inevitably an increased weight which may give rise to a problem in regard to the drive of the head arm.
On the other hand, in the prior art method disclosed in JP-A-61-16076 cited above, the off-track attributable to the difference between the amounts of thermal expansion of various parts of the magnetic disk drive is compensated by causing deformation of the head arm. More concretely, a member having a coefficient of thermal expansion different from that of the head arm is combined with the head arm as described above so as to provide the head arm with the function of a bimetal, thereby forcedly causing deformation of the head arm in the out-of-plane direction, that is, in the axial direction of the spindle supporting magnetic disks. However, even when deformation of a part of the magnetic disk drive due to the difference between the amounts of thermal expansion of various parts of the magnetic disk drive. (for example, tilting of the spindle) is to be compensated by deformation of each of the head arms, the coefficient of thermal expansion of the member combined with one of the head arms must be selected to be different from that of the member combined with another head arm, because the amount of compensation by the latter head arm differs from that of compensation by the former head arm. Such a magnetic disk drive will not be fully satisfactorily usable for general purposes.